I. Scott MacKenzie

Who they are

MacKenzie is a researcher in human-computer interaction. The Why We Project cites him for two papers, and this page is limited to what those papers report. His wider biography is not covered here.

Key papers

MacKenzie (1992), Fitts' law as a research and design tool in human-computer interaction, Human-Computer Interaction, volume 7, issue 1.

Soukoreff and MacKenzie (2004), Towards a standard for pointing device evaluation, perspectives on 27 years of Fitts' law research in HCI, International Journal of Human-Computer Studies, volume 61, issue 6.

Key ideas

The 1992 paper places Fitts's law in its historical and theoretical context and examines problems that arise when observations keep departing from its predictions. It proposes a revised index of task difficulty, the logarithm of the distance-to-width ratio plus one, which it argues is more soundly based in information theory than Fitts's original and which cannot return a negative value when targets overlap. It then reviews six studies that used the law to predict cursor-positioning and selection times with mice, trackballs, joysticks, touchpads, helmet-mounted sights and eye trackers. Their performance measures varied enormously, which made cross-study comparison difficult, and the paper identifies sources of experimental variation that might account for the differences.

It also describes the index of performance as analogous to channel capacity and as the reciprocal of the slope of the fitted line.

The 2004 review

The abstract of the 2004 article, hosted on MacKenzie's university page, says the paper offers seven recommendations for researchers who build Fitts's law models, whether to predict movement time or to compare experimental conditions. The recommendations support and extend the ISO standard for evaluating pointing devices, known as ISO 9241-9. The authors argue that following them would improve the robustness and comparability of later research. They also review 24 published Fitts's law models of the mouse and nine studies that used the ISO standard.

The stated aim is convergence. The authors want the field to work to a shared standard so that device studies from different laboratories can be set side by side, instead of each adding its own variant of the law. At the time of that article both authors were affiliated with the Department of Computer Science and Engineering at York University in Toronto. This page does not state his current position.

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